EXPERIMENTAL EVOLUTION 



117 



Since that time, both the new forms have more or less 

 spread over the field" (de Vries). 



Another mutant of 0. Lamarckiana was called by 

 de Vries (Enothera gigas (Fig. 62). The cells of this 

 mutant have twice as many chromosomes as the parent 

 form. 



FIG. 62. Giant evening-primrose (Enothera gigas, a mutant from 

 (Enotheta Lamarckiana, originated in 1895. Cf. Fig. 61. (After de 

 Vries.) 



92. The Test of a Mutation. The deciding test as to 

 whether a given new form, arising without crossing from 

 a form that has bred true for at least two generations, is 

 really a mutant or merely a fluctuating variant, is to see 

 if it breeds true to seed for the new character or characters. 



